New York Times

WASHINGTON — The Supreme Court agreed Tuesday to hear a major challenge to the limits set by the Obama administration on emissions of mercury and other toxic pollutants from coal-fired power plants.

It is the latest effort by industry groups to roll back regulations that would reduce emissions like mercury, soot, sulfur, smog and carbon dioxide. The case also threatens to undermine one of the administration’s most significant victories and chip away at President Obama’s legacy.

John Walke, a lawyer with the Natural Resources Defense Council, called the regulation of mercury emissions that are at issue in the new case “the greatest clean air achievement of the Obama administration’s first term.”

The industry groups say the Environmental Protection Agency is overstepping its authority under the Clean Air Act by issuing the series of regulations. Republicans have attacked the rules as a “war on coal” and an example of what they say is the executive branch’s overreach.

The basic question in the new case is whether and when the E.P.A. must take regulation costs into account. The agency’s interpretation is that the Clean Air Act, which requires regulations to be “appropriate and necessary,” does not demand that costs be taken into consideration early in the regulatory process.

In the Supreme Court term that ended in June, the justices heard cases filed by industry groups against two of the Obama administration’s environmental regulations — one aimed at limiting power plant pollution that wafts across state lines, the other at cutting planet-warming greenhouse gas emissions.

The E.P.A. won the first case and largely prevailed in the second, though the Supreme Court indicated that it remained prepared to impose limits on the agency’s regulatory authority.

The case against the mercury pollution rule is likely to be followed by more fights. The E.P.A. on Wednesday will release a regulation to cut ozone pollution. Next year, the agency is scheduled to finalize rules that would slash greenhouse gas emissions from power plants. Environmental law experts say the Supreme Court’s decision in the mercury case may provide some hints about how those other rules might fare.

“Is this part of a larger trend of the Supreme Court exerting greater authority over E.P.A.’s regulations?” asked Roger R. Martella Jr., a general counsel at the agency during President George W. Bush’s administration. The new case is a challenge by more than 20 states, along with industry groups and energy companies.

A divided three-judge panel of the United States Court of Appeals for the District of Columbia Circuit ruled in April that the agency’s interpretation of the act was reasonable.

“For E.P.A. to focus its ‘appropriate and necessary’ determination on factors relating to public health hazards, and not industry’s objections that emission controls are costly, properly puts the horse before the cart,” Judge Judith W. Rogers wrote for the majority.

In dissent, Judge Brett M. Kavanaugh said that in context, the statute required attention to costs “as a matter of common sense, common parlance, and common practice.”

“To be sure,” he continued, “E.P.A. could conclude that the benefits outweigh the costs. But the problem here is that E.P.A. did not even consider the costs. And the costs are huge, about $9.6 billion a year — that’s billion with a ‘b’ — by E.P.A.’s own calculation.”

In its petition seeking review of the appeals court’s ruling, the National Mining Association said the mercury regulation’s costs far outweighed its benefits.

“No rational person,” the group’s brief said, “would see spending $9.6 billion for $4 million to $6 million in return as an appropriate exchange.”

In response, the agency said it took costs into account later in the regulatory process. Its brief said that it considered “compliance costs when establishing the appropriate level of any power plant regulation, but not when deciding whether to regulate those plants” at all.

The agency also disputed the mining group’s calculations. Once fully in place in 2016, the regulations would yield benefits that could total as much as $90 billion, the E.P.A. said in its brief.

“Those quantifiable benefits,” it said, “include the prevention of up to 11,000 premature deaths each year and the prevention of I.Q. loss to children whose mothers consume noncommercial freshwater fish caught by recreational anglers in modeled watersheds during pregnancy.”

The cases the Supreme Court agreed to hear are Michigan v. Environmental Protection Agency, No. 14-46; Utility Air Regulatory Group v. Environmental Protection Agency, No. 14-47; and National Mining Association v. Environmental Protection Agency, No. 14-49. The court consolidated the cases for a single one-hour argument.

In its order granting review of the cases, the court sharpened and streamlined the issue it would consider: “whether the Environmental Protection Agency unreasonably refused to consider costs in determining whether it is appropriate to regulate hazardous air pollutants emitted by electrical utilities.”